1. Field of the Invention
The invention relates to systems for cardiopulmonary bypass, and more particularly to systems that provide hemodynamic and veno-arterial cardiopulmonary support.
2. Discussion of Related Art
Patients in circulatory dysfunction, for example, prospective organ transplant patients, often require a circulatory support system. In the case of a patient awaiting an organ transplant, such a system would be used as a "bridge-to-transplant"; that is, the system would be adapted to provide circulatory support until a donor organ could be obtained. As used in this specification, the term "bridge-to-transplant" generically refers to the function of providing circulatory assistance in the presence of cardiac dysfunction, or other circulatory dysfunction.
Typical cardiopulmonary bypass systems are rather complex, and generally are not particularly well-adapted for applications such as the "bridge-to-transplant." Moreover, most standard systems exhibit poor hemodynamic characteristics. That is, such systems typically cause too much damage to the blood to be useful for extended periods.
For example, typical cardiopulmonary bypass systems are disclosed in U.S. Pat. No. 3,890,969 to Fischel, U.S. Pat. No. 4,466,804 to Hino, and U.S. Pat. No. 4,610,656 to Mortensen. Such conventional systems commonly utilize several pumps, a venous reservoir, an arterial reservoir, and a separate bubble-trapping device.
These conventional systems exhibit several disadvantages. The most apparent disadvantage is the overall complexity of such systems. For example, the pumps may need to be synchronized with each other, or each of the reservoirs or bubble traps may need a special support frame. Also, the numerous components require extensive tubing and interconnections.
The complexity of the conventional systems leads to higher costs of manufacture and operation. Also, the more complex systems may take longer to set up, and system set-up may require expert personnel and supervision. Even with such expert personnel present, the system's complexity increases the risk of error in setting up the system. Likewise, once in operation, a conventional system requires continuous monitoring and adjustment by expert personnel.
Moreover, conventional cardiopulmonary bypass systems are not usable for long-term application because they significantly damage the blood after a fairly short use (e.g., 6-8 hours). For instance, conventional occlusive roller pumps mechanically destroy red blood cells, and centrifugal pumps expose blood elements to high shear forces, which also destroy red blood cells. This "blood trauma" can occur in any cardiopulmonary bypass system. It is caused and/or aggravated by occlusive or high-shear pumps, interconnections and other system components likely to increase system pressure or turbulence.
The above factors illustrate the desirability of a simple cardiopulmonary bypass system with relatively few components. Devices similar to that disclosed in U.S. Pat. No. 4,540,399 to Litzie et al. represent an attempt to achieve such simplicity. Litzie et al. disclose an emergency bypass system with one non-occlusive pump, an oxygenator, and a separate bubble trap. The Litzie patent specifies a centrifugal rotor-type pump connected proximal (i.e., on the venous side) to the oxygenator.
The Litzie et al. patent teaches a simplified cardiopulmonary bypass system compared to other known systems. However, the Litzie et al. system requires the bubble-trapping device in addition to the pump and oxygenator.
Also, the pump disclosed in Litzie et al. operates on the principle of high shear forces. As noted above, exposing the blood elements to these high shear forces cause significant damage to the blood.
The advent and increasing use of cardiac transplantation as a formal treatment has brought about the need for a circulatory support system capable of supporting a patient in circulatory dysfunction for some length of time until a donor organ can be obtained. Such a circulatory support system would also be quite useful in numerous other situations, such as (1) where the patient is in a state of cardiogenic shock; (2) where the patient is in a state of septic shock, (3) for postcardiotomy weaning from the bypass; and (4) for assisting the circulatory system to avoid an impending myocardial infarction. It is highly desirable to simplify the system as much as possible.